Studies are continuing on the pharmacokinetics and biotransformation of LAAM. Intravenous administration of 0.5 mg/kg doses of (3H) acetylnormethadol in 4 monkeys produced plasma levels of 222.4 plus or minus 43 ng/ml at 5 min. which were more or less sustained up to 20 min. and declined to (mean plus or minus S.E.M.) 53 plus or minus 14, 6 plus or minus 1 and 2 plus or minus 0.5 ng/ml at 6, 24 and 48 hrs. respectively after injection. Acetylnormethadol was not detectable in plasma 96 hrs. after injection but non-extractable polar metabolites amounting to 37 plus or minus 9 ng-equivalent/ml were present at this time in plasma. Acetylnormethadol was extensively metabolized in the monkey on administration by the i.v. route and 1.2 plus or minus 0.1 and 5.3 plus or minus 0.9 (mean plus S.E.M.) percent of dose were excreted unchanged in urine and feces over a period of 1 week. Major excretion of radioactivity occurred in feces within 48 hrs. of the injection. Non-extractable polar metabolites of acetylnormethadol constituted the major amount of the excreted dose 23.1 plus or minus 5.3% in urine and 48.4% plus or minus of dose in feces. The same 4 monkeys used in intravenous studies were administered a single 0.5 mg/kg dose of (3H) acetylnormethadol and plasma obtained at different times after administration were analyzed for free acetylnormethadol. These studies have shown peak plasma values of 12-20 ng/ml between 2 to 4 hrs. after oral administration which then declined to approximately 4 and 2 ng/ml at 24 and 48 hrs. respectively after drug administration. As in i.v. experiments, the drug was not detectable in plasma 96 hrs. after oral administration. Approximate percentages of the dose excreted unchanged in urine feces amounted to 2.5 and 11-21 respectively over a period of 1 week after oral administration.